There is a technique of displaying blood flow information of a patient as an image by a so-called ultrasonic Doppler method of obtaining blood flow information of a patient by using the Doppler effect of an ultrasonic wave. In this technique, blood flow information of a patient is displayed as a Doppler spectral image defined by the blood flow velocity along the ordinate and the time along the abscissa. However, since the blood flow velocity changes depending on the measurement position and patient, it is necessary to adjust the measurement range (scale) of the blood flow velocity and a reference line (baseline) indicating a blood flow velocity of 0 in order to display the entire waveform. In the conventional technique, the operator presses an automatic adjustment button provided on the ultrasonic diagnostic apparatus to automatically adjust the scale and baseline, and display the entire waveform. In this technique, for example, the maximum amplitude of a waveform is estimated based on the maximum or minimum value of a blood flow velocity measured until the button is pressed, and the scale and baseline are adjusted.
However, in the conventional technique, the operator needs to take the trouble to press the automatic adjustment button, and this is cumbersome to the operator. When the operator wants to check the entire waveform soon and presses the automatic adjustment button before measuring the actual maximum and minimum values of the blood flow velocity, more specifically, before the lapse of the time of one heart beat, the scale and baseline are adjusted based on the maximum or minimum value of the blood flow velocity until he pressed the automatic adjustment button. As a result, the entire waveform may not be displayed.